Pressure-sensitive adhesive for polarizing plates, polarizing plate with pressure-sensitive adhesive and production process for the same

ABSTRACT

Provided are a pressure-sensitive adhesive for polarizing plates which can apply a polarizing plate on a liquid crystal cell with good adhesion and has the characteristic that a liquid crystal display device obtained therefrom is less liable to cause light leakage even under the environment of high temperature and high humidity and which has a removability and a polarizing plate with the above pressure-sensitive adhesive and a production process for the same. 
     The pressure-sensitive adhesive for polarizing plates is prepared by irradiating a pressure-sensitive adhesive material comprising (A) an acrylic base polymer comprising a monomer having a carboxyl group in a monomer composition ratio of 0.5 mass % or less and (B) an active energy beam-curable compound with an active energy beam, and it has a storage elastic modulus (G′) of 0.3 MPa or more at 23° C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pressure-sensitive adhesive forpolarizing plates, a polarizing plate with the pressure-sensitiveadhesive and a production process for the same, and an optical filmusing the above polarizing plate with the pressure-sensitive adhesiveand a production process for the same. More specifically, the presentinvention relates to a pressure-sensitive adhesive for polarizing plateswhich is suitably applied to a polarizing plate, particularly apolarizing plate integrated with a viewing angle expanding film or apolarizing plate comprising a retardation film laminated thereon and canapply the above polarizing plate on a liquid crystal cell with goodadhesion and which has the characteristic that a liquid crystal displayobtained therefrom is less liable to cause light leakage even under theenvironment of high temperature and high humidity and can readily bepeeled off when applied mistakenly, a polarizing plate with the abovepressure-sensitive adhesive and a production process for the same and anoptical film and a production process for the same.

2. Description of the Related Art

When a sheet comprising organic materials is applied on an adherend suchas glass, ceramic and metal via a pressure-sensitive adhesive, theunfavorable situation that peeling of the sheet in an end part orlifting thereof is caused with the passage of time has so far frequentlybeen brought about.

In order to solve the above situation, usually used is a stronglypressure-sensitive adhesive material in which an adhesive performance isenhanced by raising a molecular weight of a component constituting apressure-sensitive adhesive or elevating a cross-linking densitythereof. However, while the holding power is improved when using theabove strongly pressure-sensitive adhesive material, thepressure-sensitive adhesive can not follow a change in the shape whichis caused by shrinkage or swelling of the sheet comprising organicmaterials under the environment of high temperature and high humidity,and it is a factor to bring about various troubles.

On the other hand, those in which a polarizing plate is applied on asurface thereof are included in optical parts, and a representativeexample thereof includes a liquid crystal cell of a liquid crystaldisplay (LCD). It shall be explained below with reference to FIG. 1.

This liquid crystal cell 13 has usually a structure in which twotransparent electrode substrates having orientation layers formedthereon are disposed with the orientation layers turned to an inside sothat a prescribed interval is formed by spacers and the peripherythereof is sealed to interpose a liquid crystal material in the aboveinterval and in which polarizing plates 11 are disposed respectively onthe two transparent electrode substrates described above viapressure-sensitive adhesives 12. In general, the polarizing platedescribed above comprises a polarizing film having a three layerstructure in which optically isotropic films, for example, triacetylcellulose (TAC) films are adhered on both surfaces of a polyvinylalcohol base polarizer, and a pressure-sensitive adhesive layer isfurther provided on the other surface thereof for the purpose ofapplying on an optical part such as a liquid crystal cell.

Further, as shown in a schematic drawing of FIG. 2, a retardation film24 is disposed in a certain case between a polarizing plate 21 and aliquid crystal cell 23 via pressure-sensitive adhesives 22 and 25 inorder to improve the viewing angle characteristics.

When applying a polarizing plate having the constitution described aboveto an optical part such as a liquid crystal cell or applying apolarizing plate to a retardation film, it results in assuming amultilayer structure comprising different kinds of the materials and isshort of a dimensional stability, and a change in the dimension causedby shrinkage and swelling is increased particularly under theenvironment of high temperature and high humidity. In general, thestrongly pressure-sensitive adhesive described above is used as apressure-sensitive adhesive for the above polarizing plate, andtherefore lifting and peeling brought about by a change in a dimensionof the polarizing plate can be inhibited. However, a stress broughtabout by a change in a dimension of the above polarizing plate can notbe absorbed by the pressure-sensitive adhesive layer to make a residualstress in the polarizing plate uneven. As a result thereof, broughtabout are the problems that liable to be produced are so-called “lightleakage” in a TN liquid crystal cell and “uneven color” in STN liquidcrystal.

In order to solve the problems described above, disclosed is a techniquein which a pressure-sensitive adhesive is suitably softened and providedwith a stress relaxing property by adding a low molecular weightsubstance such as a plasticizer to a pressure-sensitive adhesive (referto, for example, a patent document 1). However, addition of the lowmolecular weight substance causes stain of the adherend when peeling offthe polarizing plate and, in addition thereto, lowers the holding power,and lifting and peeling brought about by the passage of time are liableto be caused.

On the other hand, disclosed is a pressure-sensitive adhesive sheetobtained by radiation-induced cross-linking a mixture comprising anacrylic base copolymer (A) and an acrylic base polymer (B) having aradiation-polymerizable group in a side chain in a proportion of 100:1to 100:100 in terms of a weight ratio (refer to, for example, a patentdocument 2).

In the above patent document, examples are described for polarizingplates, but a size of samples evaluated for a light leaking property isnot described in any of the examples. The present inventors evaluated alight leaking property of a polarizing plate having a 15 inch size usingthe pressure-sensitive adhesives described in the examples of the abovepatent document, and the results thereof were not sufficientlysatisfactory.

As described above, it is difficult to allow an adhesion durability tobe consistent with a light leakage preventing property in apressure-sensitive adhesive for a polarizing plate, and it is a subjectto allow them to stand together.

In a production step of a liquid crystal display and the like, when anapplying position is deviated in applying a polarizing plate on anoptical part such as a liquid crystal cell, the polarizing plate has tobe peeled off in a certain case after some time passes since applied toreuse the expensive liquid crystal cell. Accordingly, required is such apressure-sensitive adhesive that a polarizing plate can relativelyreadily be peeled off from a liquid crystal cell even after some timepasses since applied on the liquid crystal cell via thepressure-sensitive adhesive coated on the polarizing plate. This is aproperty which is contradictory to strengthening of an adhesive strengthfor providing an adhesion durability, and it is a subject to allow themto stand together.

Patent document 1: Japanese Patent No. 3272921 Patent document 2:Japanese Patent Application Laid-Open No. 107005/2001 SUMMARY OF THEINVENTION

In light of the situation described above, an object of the presentinvention is to provide a pressure-sensitive adhesive for polarizingplates which is suitably applied to a polarizing plate, particularly apolarizing plate integrated with a viewing angle expanding film or apolarizing plate comprising a retardation film laminated thereon and canapply the above polarizing plate on a liquid crystal cell with goodadhesion and which has the characteristic that a liquid crystal displaydevice obtained therefrom is less liable to cause light leakage evenunder the environment of high temperature and high humidity and canreadily be removed (hereinafter referred to merely as “remove”) from theliquid crystal cell even after some time passes since applied and apolarizing plate with the above pressure-sensitive adhesive.

Intensive researches repeated by the present inventors in order todevelop a pressure-sensitive adhesive for polarizing plates having thecharacteristics described above have resulted in finding that the aboveobject can be achieved by a pressure-sensitive adhesive for polarizingplates which is obtained by irradiating a pressure-sensitive adhesivematerial comprising a specific acrylic base copolymer and an activeenergy beam-curable compound with an active energy beam.

Further, the present inventors have found that the polarizing plate withthe pressure-sensitive adhesive described above can efficiently beproduced by applying a polarizing plate on a pressure-sensitive adhesivematerial layer provided on a release layer of a release sheet andirradiating a release sheet side with an active energy beam.

The present invention has been completed based on the above knowledge.

That is, the present invention provides:

(1) a pressure-sensitive adhesive for polarizing plates, which isprepared by irradiating a pressure-sensitive adhesive materialcomprising (A) an acrylic base polymer comprising a monomer having acarboxyl group in a monomer composition ratio of 0.5 mass % or less and(B) an active energy beam-curable compound with an active energy beamand which has a storage elastic modulus (G′) of 0.3 MPa or more at 23°C.,(2) the pressure-sensitive adhesive for polarizing plates as describedin the above item (1), wherein the storage elastic modulus (G′) at 23°C. is 0.3 to 15 MPa,(3) the pressure-sensitive adhesive for polarizing plates as describedin the above item (1) or (2), wherein the storage elastic modulus (G′)at 80° C. is 0.3 MPa or more,(4) the pressure-sensitive adhesive for polarizing plates as describedin the above item (3), wherein the storage elastic modulus (G′) at 80°C. is 0.3 to 10 MPa,(5) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (4), wherein it is used for applying apolarizing plate on a liquid crystal glass cell,(6) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (5), wherein the active energybeam-curable compound of the component (B) is a multifunctional(meth)acrylate base monomer having a molecular weight of less than 1000,(7) the pressure-sensitive adhesive for polarizing plates as describedin the above item (6), wherein the multifunctional (meth)acrylate basemonomer has a cyclic structure,(8) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (7), wherein a content proportion ofthe component (A) to the component (B) is 100:1 to 100:100 in terms of amass ratio,(9) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (8), wherein the pressure-sensitiveadhesive material further comprises (C) a cross-linking agent,(10) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (9), wherein the pressure-sensitiveadhesive material further comprises (D) a silane coupling agent,(11) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (10), wherein the adhesive strength tonon-alkali glass is 0.2 to 20 N/25 mm,(12) the pressure-sensitive adhesive for polarizing plates as describedin the above item (11), wherein a rise percentage of the adhesivestrength to non-alkali glass after 168 hours pass since applied is 20%or less based on the initial value,(13) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (12), wherein the maximum shear load ata distortion of 4000% or less in applying the polarizing plate onnon-alkali glass at an applying area of 100 mm² (10 mm×10 mm) andmeasuring a shear load at a shearing rate of 0.1 mm/minute is 70 N orless,(14) the pressure-sensitive adhesive for polarizing plates as describedin any of the above items (1) to (13), wherein a gel ratio is 85% ormore,(15) a polarizing plate with a pressure-sensitive adhesive,characterized by having a layer comprising the pressure-sensitiveadhesive as described in any of the above items (1) to (14) on apolarizing plate,(16) a production process for the polarizing plate with thepressure-sensitive adhesive as described in the above item (15),comprising applying a polarizing plate on a pressure-sensitive adhesivematerial layer provided on a release layer of a release sheet and thenirradiating a release sheet side with an active energy beam and (17) apressure-sensitive adhesive sheet prepared by interposing thepressure-sensitive adhesive for polarizing plates as described in any ofthe above items (1) to (14) between two release sheets so that thepressure-sensitive adhesive is brought into contact with release layersides of the release sheets.

According to the present invention, capable of being provided are apressure-sensitive adhesive for polarizing plates which is suitablyapplied to a polarizing plate, particularly a polarizing plateintegrated with a viewing angle expanding film or a polarizing platecomprising a retardation film laminated thereon and can apply the abovepolarizing plate on a liquid crystal cell with good adhesion and whichhas the characteristic that a liquid crystal display obtained therefromis less liable to cause light leakage even under the environment of hightemperature and high humidity and can relatively readily be peeled offfrom a liquid crystal cell even after some time passes since applied anda polarizing plate with the above pressure-sensitive adhesive.

Further, according to the present invention, a process for efficientlyproducing the polarizing plate with the pressure-sensitive adhesivedescribed above can be provided.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is an outline drawing showing a constitution of LCD.

FIG. 2 is an outline drawing showing a constitution of LCD.

FIG. 3 is an explanatory drawing showing a method for evaluating a lightleaking property of the polarizing plates provided with thepressure-sensitive adhesive obtained in the examples and the comparativeexamples.

EXPLANATIONS OF THE CODES

-   1, 2: Liquid crystal displays-   11, 21: Polarizing plates-   12, 22, 25: Pressure-sensitive adhesives-   13, 23: glass (liquid crystal cells)-   24: Retardation film

DETAILED DESCRIPTION OF THE INVENTION

The pressure-sensitive adhesive of the present invention for polarizingplates is a pressure-sensitive adhesive for polarizing plates, which isprepared by irradiating a pressure-sensitive adhesive materialcomprising (A) an acrylic base polymer comprising a monomer having acarboxyl group in a monomer composition ratio of 0.5 mass % or less and(B) an active energy beam-curable compound with an active energy beam.

A (meth)acrylic ester polymer can be given as the acrylic base polymerof the component (A). In the present invention, (meth)acrylic estermeans both acrylic ester and methacrylic ester. The same shall apply toother similar terms. The polymer means both a “homopolymer” and a“copolymer”.

The component (A) in the present invention is characterized bycomprising a monomer having a carboxyl group in a monomer compositionratio of 0.5 mass % or less. Usually, in order to provide apressure-sensitive adhesive with a strong pressure-sensitive adhesiveproperty, a monomer having a cross-linking point represented by acarboxyl group is copolymerized with a (meth)acrylic ester monomerhaving no cross-linking point to obtain a (meth)acrylic ester basecopolymer, and this is used as a principal agent for apressure-sensitive adhesive. In contrast with this, the acrylic basepolymer (A) comprises a monomer having a carboxyl group in a monomercomposition ratio of 0.5 mass % or less, and it is preferably a polymerof a (meth)acrylic ester monomer having no carboxyl group.

Controlling a content of the monomer having a carboxyl group to 0.5 mass% or less makes it possible to secure the removability which is theobject of the present invention. The monomer having a carboxyl groupincludes (meth)acrylic acid, crotonic acid, maleic acid and itaconicacid.

A polymer of (meth)acrylic ester in which an alkyl group of an esterpart has 1 to 20 carbon atoms can preferably be given as the(meth)acrylic ester polymer. In this regard, the examples of the(meth)acrylic ester in which an alkyl group of an ester part has 1 to 20carbon atoms include methyl (meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, butyl(meth)acrylate, pentyl (meth)acrylate,hexyl(meth)acrylate, cyclohexyl (meth)acrylate,2-ethylhexyl(meth)acrylate, isooctyl (meth)acrylate,decyl(meth)acrylate, dodecyl (meth)acrylate, myristyl(meth)acrylate,palmityl (meth)acrylate and stearyl(meth)acrylate. They may be usedalone or in combination of two or more kinds thereof.

Among the above compounds, ethyl(meth)acrylate and butyl(meth)acrylateare particularly preferred in terms of readily controlling a molecularweight in producing the polymer.

The (meth)acrylic acid ester polymer described above may contain acopolymerizable component as a constitutional component as long as theeffects of the present invention are not damaged. To be specific, it isa monomer having a hydroxyl group, an amino group and an amide group asa functional group, and the specific examples thereof includehydroxyalkyl(meth)acrylates such as 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate,2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl(meth)acrylate and4-hydroxybutyl(meth)acrylate; acrylamides such as acrylamide,methacrylamide, N-methylacrylamide, N-methylmethacrylamide,N-methylolacrylamide and N-methylolmethacrylamide; and (meth)acrylicacid monoalkylamino esters such as monomethylaminoethyl (meth)acrylate,monoethylaminoethyl(meth)acrylate, monomethylaminopropyl(meth)acrylateand monoethylaminopropyl(meth)acrylate. The above monomers may be usedalone or in combination of two or more kinds thereof.

In the above pressure-sensitive adhesive material, the (meth)acrylicester polymer used as the component (A) has preferably a molecularweight of 500,000 or more in terms of a weight average molecular weight.If the weight average molecular weight is 500,000 or more, the adhesionwith an adherend and the adhesive durability under high temperature andhigh humidity are satisfactory, and lifting and peeling are not broughtabout. Considering the adhesion and the adhesive durability, the aboveweight average molecular weight is preferably 1,000,000 to 2,200,000,particularly preferably 1,200,000 to 2,000,000. The molecular weightdistribution (Mw/Mn) showing a proportion of a weight average molecularweight (Mw) to a number average molecular weight (Mn) is preferably 20or less. If the molecular weight distribution is 20 or less, thesatisfactory adhesive durability is obtained.

The weight average molecular weight and the number average molecularweight described above are values reduced to polystyrene which aremeasured by gel permeation chromatography (GPC).

In the above pressure-sensitive adhesive material, the (meth)acrylicester polymer of the component (A) may be used alone or in combinationof two or more kinds thereof.

In the pressure-sensitive adhesive material of the present invention, amultifunctional (meth)acrylate base monomer having a molecular weight ofless than 1000 can preferably be given as the active energy beam-curablecompound used as the component (B).

The above multifunctional (meth)acrylate base monomer having a molecularweight of less than 1000 includes, for example, a difunctional type suchas 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentylglycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate,caprolactone-modified dicyclopentenyl di(meth)acrylate, ethyleneoxide-modified phosphoric acid di(meth)acrylate, di(meth)acryloxyethylisocyanurate, allylated cyclohexyl di(meth)acrylate,tricyclodecanedimethanol (meth)acrylate, dimethyloldicyclopentanedi(meth)acrylate, ethylene oxide-modified hexahydrophthalic aciddi(meth)acrylate, neopentyl glycol-modified trimethylpropanedi(meth)acrylate, adamantane di(meth)acrylate and9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene; a trifunctional typesuch as trimethylolpropane tri(meth)acrylate, dipentaerythritoltri(meth)acrylate, propionic acid-modified dipentaerythritoltri(meth)acrylate, pentaerythritol tri(meth)acrylate, propyleneoxide-modified trimethylolpropane tri(meth)acrylate andtris(meth)acryloxyethyl isocyanurate; a tetrafunctional type such asdiglycerin tetra(meth)acrylate and pentaerythritol tetra(meth)acrylate;a pentafunctional type such as propionic acid-modified dipentaerythritolpenta(meth)acrylate; and a hexafunctional type such as dipentaerythritolhexa(meth)acrylate and caprolactone-modified dipentaerythritolhexa(meth)acrylate.

In the present invention, only one kind of the above multifunctional(meth)acrylate base monomers may be used alone or they may be used incombination of two or more kinds thereof. Among them, those having acyclic structure in a skeleton structure are preferably containedtherein. The cyclic structure may be a carbocyclic structure or aheterocyclic structure and may be a monocyclic structure or a polycyclicstructure. Suited as the above multifunctional (meth)acrylate basemonomer are, for example, those having an isocyanurate structure such asdi(meth)acryloxyethyl isocyanurate and tris(meth)acryloxyethylisocyanurate, dimethyloldicyclopentane di(meth)acrylate, ethyleneoxide-modified hexahydrophthalic acid di(meth)acrylate,tricyclodecanedimethanol (meth)acrylate, neopentyl glycol-modifiedtrimethylolpropane di(meth)acrylate and adamantane di(meth)acrylate.

An acrylate base oligomer of an active energy beam-curable type can beused as the component (B). The above acrylate base oligomer haspreferably a weight average molecular weight of 50,000 or less. Theexamples of the above acrylate base oligomer include polyesteracrylates, epoxy acrylates, urethane acrylates, polyether acrylates,polybutadiene acrylates and silicone acrylates.

In this respect, the polyester acrylate base oligomers are obtained, forexample, by esterifying the hydroxyl groups of a polyester oligomerhaving hydroxyl groups at both ends which is obtained by condensation ofpolyvalent carboxylic acid and polyhydric alcohol with (meth)acrylicacid or by esterifying a hydroxyl group at an end of an oligomerobtained by adding alkylene oxide to polyvalent carboxylic acid with(meth)acrylic acid. The epoxy acrylate base oligomers are obtained, forexample, by reacting an oxirane ring of a bisphenol A type epoxy resinor a novolak type epoxy resin having a relatively low molecular weightwith (meth)acrylic acid and esterifying it. Further, capable of beingused as well are epoxy acrylate oligomers of a carboxyl-modified typeobtained by modifying partially the above epoxy acrylate base oligomerswith dibasic carboxylic anhydride. The urethane acrylate base oligomersare obtained, for example, by esterifying a polyurethane oligomerobtained by reacting polyetherpolyol or polyesterpolyol withpolyisocyanate with (meth)acrylic acid, and the polyol acrylate baseoligomers are obtained by esterifying a hydroxyl group ofpolyetherpolyol with (meth)acrylic acid.

A weight average molecular weight of the acrylate base oligomersdescribed above is selected in a range of preferably 50,000 or less,more preferably 500 to 50,000 and further preferably 3,000 to 40,000 interms of a value reduced to standard polymethyl methacrylate.

The above acrylate base oligomers may be used alone or in combination oftwo or more kinds thereof.

In the present invention, an adduct acrylate base polymer in which agroup having a (meth)acryloyl group is introduced into a side chain canalso be used as the component (B). The above adduct acrylate basepolymer can be obtained by using a copolymer of (meth)acrylic esterexplained in the (meth)acrylic ester polymer of the component (A) with amonomer having a functional group in a molecule to react a part of thefunctional group of the above copolymer with a compound having a(meth)acryloyl group and a group which reacts with the above functionalgroup. A weight average molecular weight of the above adduct acrylatebase polymer is usually 500,000 to 2,000,000 in terms of a value reducedto polystyrene.

In the present invention, one suitably selected from the multifunctionalacrylate base monomer, the acrylate base oligomer and the adductacrylate base polymer each described above may be used as the component(B) or two or more kinds selected from them may be used in combination.

In the present invention, a content ratio of the acrylic polymer of thecomponent (A) to the active energy beam-curable compound of thecomponent (B) falls in a range of preferably 100:1 to 100: 100, morepreferably 100:5 to 100:50 and further preferably 100:10 to 100:40 interms of mass ratio from the viewpoint of the performances of thepressure-sensitive adhesive obtained.

A photopolymerization initiator can be added, if necessary, to thepressure-sensitive adhesive material in the present invention. The abovephotopolymerization initiator includes, for example, benzoin, benzoinmethyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoinn-butyl ether, benzoin isobutyl ether, acetophenone,dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone,2-hydroxy-2-methyl-1-phenylpropane-1-one, 1-hydroxycyclohexyl phenylketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one,4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl) ketone, benzophenone,p-phenylbenzophenone, 4,4′-diethylaminobenzophenone,dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone,2-tertiary-butylanthraquinone, 2-aminoanthraquinone,2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethylketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ester,oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] and2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide. They may be used aloneor in combination of two or more kinds thereof. A blending amountthereof is selected usually in a range of 0.2 to 20 mass parts per 100parts of the component (B) described above.

A cross-linking agent can be added, if necessary, as a component (C) tothe pressure-sensitive adhesive material in the present invention. Theabove cross-linking agent shall not specifically be restricted, andoptional ones suitably selected from those which have so farconventionally been used as a cross-linking agent in acrylic basepressure-sensitive adhesives can be used. The above cross-linking agentincludes, for example, polyisocyanate compounds, epoxy resins, melamineresins, urea resins, dialdehydes, methylol polymers, aziridine basecompounds, metal chelate compounds, metal alkoxides and metal salts, andthe polyisocyanate compounds are preferably used.

In this respect, capable of being given as the polyisocyanate compoundsare aromatic polyisocyanates such as tolylenediisocyanate,diphenylmethanediisocyanate and xylylenediisocyanate, aliphaticpolyisocyanates such as hexamethylenediisocyanate, alicyclicpolyisocyanates such as isophoronediisocyanate and hydrogenateddiphenylmethanediisocyanate, buret bodies and isocyanurate bodiesthereof and adduct bodies which are reaction products thereof with lowmolecular active hydrogen-containing compounds such as ethylene glycol,propylene glycol, neopentyl glycol, trimethylolpropane and castor oil.

In the present invention, the cross-linking agent described above may beused alone or in combination of two or more kinds thereof. A use amountthereof is, though depending on the kind of the cross-linking agent,usually 0.01 to 20 mass parts, preferably 0.1 to 10 mass parts per 100mass parts of the acrylic base copolymer of the component (A) describedabove.

A silane coupling agent can be added, if necessary, as a component (D)to the pressure-sensitive adhesive material in the present invention.Addition of the above silane coupling agent improves more an adhesionbetween the pressure-sensitive adhesive and the glass cell when thepolarizing plate is applied, for example, on a liquid crystal glasscell. The above silane coupling agent is suitably an organic siliconcompound which has at least one alkoxysilyl group in a molecule andwhich is well compatible with a pressure-sensitive adhesive componentand has a light transmittance, for example, a substantially transparentcompound. An addition amount of the above silane coupling agent falls ina range of preferably 0.001 to 10 mass parts, particularly preferably0.005 to 5 mass parts per 100 mass parts of the pressure-sensitiveadhesive material (total amount of the component (A) and the component(B)).

The specific examples of the silane coupling agent described aboveinclude polymerizable unsaturated group-containing silicon compoundssuch as vinyltrimethoxysilane, vinyltriethoxysilane and3-methacryloxypropyltrimethoxysilane, silicon compounds having an epoxystructure such as 3-glycidoxypropyltrimethoxysilane and2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, amino group-containingsilicon compounds such as 3-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane andN-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane and3-chloropropyltrimethoxysilane. They may be used alone or in combinationof two or more kinds thereof.

The pressure-sensitive adhesive of the present invention for polarizingplates is prepared by irradiating the foregoing pressure-sensitiveadhesive material thus obtained with an active energy beam.

The active energy beam includes, for example, an ultraviolet ray (UVray) and an electron beam. The UV ray described above is obtained bymeans of a high pressure mercury lamp, an electrodeless lamp and a xenonlamp. On the other hand, the electron beam is obtained by means of anelectron beam accelerator. Among the above active energy beams, a UV rayis particularly suited. When using an electron beam, thepressure-sensitive adhesive can be formed without adding aphotopolymerization initiator.

A dose of the active energy beam irradiated onto the abovepressure-sensitive adhesive material is suitably selected so that thepressure-sensitive adhesive having a storage elastic modulus and anadhesive strength to non-alkali glass each described above can beobtained. In the case of a UV ray, an illuminance falls preferably in arange of 50 to 1000 mW/cm², and a light quantity falls preferably in arange of 50 to 1000 mJ/cm². In the case of an electron beam, it fallspreferably in a range of 10 to 1000 krad.

An adhesion improving agent can be added to the pressure-sensitiveadhesive material of the present invention in order to enhance anadhesion between the adhesive layer and the polarizing plate. Theadhesion improving agent includes aromatic polyisocyanates such astolylenediisocyanate, diphenylmethanediisocyanate andxylylenediisocyanate and polyisocyanate compounds such as adduct bodieswhich are reaction products of the aromatic polyisocyanates describedabove with low molecular active hydrogen-containing compounds such asethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropaneand castor oil. When functional groups are present in the acrylic basepolymer in the pressure-sensitive adhesive material, the abovepolyisocyanate compounds function as the cross-linking agent describedabove.

The pressure-sensitive adhesive of the present invention has a storageelastic modulus (G′) of 0.3 MPa or more at 23° C. If this storageelastic modulus (G′) is 0.3 MPa or more, the satisfactory lightleakage-preventing property is obtained. An upper limit of the storageelastic modulus (G′) at 23° C. shall not specifically be restricted, butit is preferably 50 MPa or less, more preferably 15 MPa or less in orderto obtain the pressure-sensitive adhesive having better adhesiondurability. From the viewpoint described above, the storage elasticmodulus (G′) at 23° C. is particularly preferably 0.35 to 12 MPa, mostpreferably 0.5 to 5 MPa. Usually, the storage elastic modulus (G′) at80° C. is preferably 0.3 MPa or more, more preferably 0.3 to 10 MPa andparticularly preferably 0.3 to 3 MPa.

The storage elastic modulus (G′) described above is a value measured bythe following method.

<Measuring Method of Storage Elastic Modulus (G′)>

The pressure-sensitive adhesive having a thickness of 30 μm is laminatedto prepare a cylindrical test piece of 8 mmφ×3 mm thickness, and astorage elastic modulus (G′) thereof is measured by a torsional shearmethod on the following conditions.

Measuring apparatus: dynamic viscoelasticity measuring apparatus“DYNAMIC ANALYZER RDAII” manufactured by Rheometric Corporation

Frequency: 1 Hz Temperature: 23° C. and 80° C.

In the pressure-sensitive adhesive of the present invention forpolarizing plates, an adhesive strength to non-alkali glass fallspreferably in a range of 0.2 to 20 N/25 mm. If this adhesive strength is0.2 N/25 mm or more, the polarizing plate can be applied on, forexample, the liquid crystal glass cell at a satisfactory adhesivestrength. On the other hand, if the above adhesive strength is 20 N/25mm or less, it is possible to remove without damaging the liquid crystalcell. In this case, the adhesive strength is an adhesive strength after24 hours pass since applied, and hereinafter the adhesive strength after24 hours pass shall be expressed as an initial value. The adhesivestrength described above is a value measured by the following method.

<Adhesive Strength to Non-Alkali Glass>

A sample having a width of 25 mm and a length of 100 mm is cut out fromthe polarizing plate with a pressure-sensitive adhesive to peel arelease sheet therefrom (thickness of an adhesive layer: 25 um) andapply the polarizing plate on non-alkali glass (“1737” manufactured byCorning Incorporated), and then it is pressurized in an autoclavemanufactured by Kurihara Manufactory Inc. on the conditions of 0.5 MPa,50° C. and 20 minutes. Thereafter, it is left standing for 24 hoursunder the environment of 23° C. and a relative humidity of 50%, and thenthe adhesive strength is measured under the above environment by meansof a tensile tester (Tensilon manufactured by Orientech Co., Ltd.) onthe conditions of a peeling rate of 300 mm/minute and a peeling angle of180°.

Further, in the pressure-sensitive adhesive of the present invention forpolarizing plates, an adhesive strength to non-alkali glass has a risepercentage of preferably 20% or less based on the initial value evenafter 168 hours pass since applied. If the rise percentage is 20% orless, the satisfactory removability is obtained.

In the pressure-sensitive adhesive of the present invention forpolarizing plates, a maximum shearing load at a distortion of 4000% orless in applying the polarizing plate on non-alkali glass at an applyingarea of 100 mm² (10 mm×10 mm) and measuring a shearing load at ashearing rate of 0.1 mm/minute is preferably 70 N or less. If themaximum shearing load is 70 N or less, the satisfactory removability isobtained. This maximum shearing load is more preferably 10 to 50 N.

The maximum shearing load described above is a value measured by thefollowing method.

<Measuring Method of Maximum Shearing Load>

A sample having a width of 10 mm and a length of 100 mm is cut out fromthe polarizing plate with the pressure-sensitive adhesive to peel arelease sheet therefrom (thickness of an adhesive layer: 25 μm) andapply the polarizing plate on an end part of non-alkali glass (“1737”manufactured by Corning Incorporated) so that an applying area is 10mm×10 mm, and then it is pressurized in an autoclave manufactured byKurihara Manufactory Inc. on the conditions of 0.5 MPa, 50° C. and 20minutes. Thereafter, it is left standing for 24 hours under theenvironment of 23° C. and a relative humidity of 50%, and then an endpart of a side in which the sample is not applied in non-alkali glassand an end part of a non-applied side in the sample are mounted in atensile tester (manufactured by Instron Corporation) under the aboveenvironment and pulled to a shearing direction at a shearing rate of 0.1mm/minute to measure a load thereof. Measurement is carried out up to adistortion amount of 4000% (deformation amount in a shearing direction:1000 μm), and a maximum load up to a deformation of 4000% is set as amaximum shearing load. The distortion is shown by a ratio of adeformation amount in a shearing direction to a thickness of theadhesive layer.

The pressure-sensitive adhesive of the present invention has preferablya gel ratio of 85% or more. That is, when an extent of a low molecularcomponent which is extracted with an organic solvent is small, lifting,peeling and stain to the adherend are small in the environment ofheating or high temperature and high humidity, and thepressure-sensitive adhesive having a gel ratio of 85% or more is high ina durability and a stability. The gel ratio is more preferably 90 to99.9%.

Various additives usually used for acrylic base pressure-sensitiveadhesives, for example, tackifiers, antioxidants, UV absorbers, lightstabilizers, softening agents, fillers and the like can be added, ifnecessary, to the pressure-sensitive adhesive of the present inventionas long as the object of the present invention is not damaged.

The pressure-sensitive adhesive of the present invention for polarizingplates is applied to a polarizing plate comprising a polarizing filmalone, and the above polarizing plate can be used for applying the abovepolarizing plate to, for example, a liquid crystal glass cell. Inparticular, the pressure-sensitive adhesive is applied to a polarizingplate in which a polarizing film is integrated with a viewing angleexpanding film, and the above polarizing plate can preferably be usedfor applying the above polarizing plate to, for example, a liquidcrystal glass cell.

The foregoing polarizing plate in which a polarizing film is integratedwith a viewing angle expanding film includes, for example, a polarizingplate in which a viewing angle expanding function layer comprising adiscotic liquid crystal is formed by coating on one face of a polarizingfilm prepared by sticking a triacetyl cellulose (TAC) film respectivelyon both faces of a polyvinyl alcohol base polarizer and a polarizingplate on which a viewing angle expanding film is stuck on one face ofabove-mentioned polarizing film with an adhesive. In this case, thepressure-sensitive adhesive is provided on the side of the viewing angleexpanding function layer or the viewing angle expanding film describedabove.

Also when a retardation film is present, as shown in FIG. 2, between apolarizing plate and a liquid crystal glass cell, the pressure-sensitiveadhesive of the present invention for polarizing plates can suitably beused. That is, a polarizing plate comprising a polarizing film alone isapplied on the retardation film with the pressure-sensitive adhesive ofthe present invention to produce an optical film, and the retardationfilm of the above optical film is applied on the liquid crystal glasscell with a pressure-sensitive adhesive. In this respect, thepressure-sensitive adhesive used for applying the retardation film onthe liquid crystal glass cell shall not specifically be restricted, anda pressure-sensitive adhesive usually used for applying a polarizingplate on a liquid crystal glass cell can be used. To be specific, itincludes a pressure-sensitive adhesive composition comprising an acrylicbase polymer, a cross-linking agent and a silane compound which isdisclosed in Japanese Patent Application Laid-Open No. 131033/1999. Thepressure-sensitive adhesive of the present invention can be used as wellfor applying a polarizing plate on a liquid crystal glass cell.

A liquid crystal display prepared by using the pressure-sensitiveadhesive of the present invention for polarizing plates to apply apolarizing plate on a liquid crystal glass cell or a retardation film inthe manner described above is less liable to cause light leakage evenunder the environment of high temperature and high humidity, and inaddition thereto, it is excellent in an adhesion durability with thepolarizing plate and the liquid crystal glass cell.

Further, the present invention provides a polarizing plate with apressure-sensitive adhesive having a layer comprising thepressure-sensitive adhesive of the present invention for polarizingplates described above on a polarizing plate. The above polarizing platemay be, as described above, a polarizing plate comprising a polarizingfilm alone, but in the case of a structure shown in FIG. 1, a polarizingplate in which a polarizing film is integrated with a viewing angleexpanding film is preferred.

A thickness of the foregoing layer comprising the pressure-sensitiveadhesive for polarizing plates is usually 5 to 100 μm, preferably 10 to50 μm and more preferably 10 to 30 μm.

A production process for the above polarizing plate with thepressure-sensitive adhesive may be any process as long as it is aprocess in which a polarizing plate provided thereon with a layercomprising the pressure-sensitive adhesive of the present invention isobtained, and it shall not specifically be restricted. According to theprocess of the present invention shown below, the desired polarizingplate with the pressure-sensitive adhesive can efficiently be produced.

In the process of the present invention, the polarizing plate is appliedon the pressure-sensitive adhesive material layer provided on therelease layer of the release sheet, and then the side of the aboverelease sheet is irradiated with an active energy beam so that thepressure-sensitive adhesive material layer is turned into a layer havingthe prescribed characteristics described above which is constituted fromthe pressure-sensitive adhesive of the present invention, whereby thepolarizing plate with the pressure-sensitive adhesive of the presentinvention is obtained.

The release sheet described above includes a sheet prepared by coating areleasing agent such as a silicone resin on a plastic film such as apolyester film of polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate or the like and a polyolefinfilm of polypropylene, polyethylene or the like to provide a releaselayer. A thickness of the above release sheet shall not specifically berestricted and is usually 20 to 150 μm.

The pressure-sensitive adhesive material and the irradiating conditionsof the active energy beam have already been explained in thepressure-sensitive adhesive of the present invention for polarizingplates described above.

Capable of being used as a method for providing the pressure-sensitiveadhesive material layer on the release sheet is, for example, a methodin which a pressure-sensitive adhesive material is coated by means of abar coating method, a knife coating method, a roll coating method, ablade coating method, a die coating method and a gravure coating methodto form a coating film and in which the coating film is dried. Thedrying conditions shall not specifically be restricted, and it is driedusually at 50 to 150° C. for 10 seconds to 10 minutes.

In the case of a constitution shown in FIG. 1, a polarizing platecomprises a polarizing film alone in many cases, and a layer comprisingthe pressure-sensitive adhesive for polarizing plates has the samethickness as described above. A production process for the polarizingplate with the pressure-sensitive adhesive in the structure shown inFIG. 1 may be any process as long as it is a process in which apolarizing plate provided thereon with a layer comprising thepressure-sensitive adhesive of the present invention is obtained as isthe case with the polarizing plate described above, and it shall notspecifically be restricted. The polarizing plate can efficiently beproduced by the production process of the present invention describedabove.

Further, in the case of the constitution shown in FIG. 2, prepared inadvance is a pressure-sensitive adhesive sheet in which thepressure-sensitive adhesive for polarizing plates described above isinterposed so that it is brought into contact with the release layersides of two release sheets, and the above pressure-sensitive adhesivesheet can be used to apply the polarizing plate on the retardation film.In this case, when the component (B) described above is used as thepressure-sensitive adhesive, an active energy beam may be irradiatedafter the pressure-sensitive adhesive is interposed between two releasesheets or the pressure-sensitive adhesive is provided on one releasesheet, and it is irradiated with the active energy beam and theninterposed with the other release sheet. The irradiation conditions ofthe active energy beam are selected so that obtained is a layer havingthe prescribed characteristics described above which is constituted fromthe pressure-sensitive adhesive of the present invention.

When the above pressure-sensitive adhesive sheet is used to produce theoptical film of the present invention, the release sheet of thepressure-sensitive adhesive sheet is peeled off, and thepressure-sensitive adhesive sheet is applied on the polarizing plate byan ordinary method.

EXAMPLES

Next, the present invention shall be explained below in further detailswith reference to examples, but the present invention shall by no meansbe restricted by these examples.

The performances of the pressure-sensitive adhesives and the polarizingplates with the pressure-sensitive adhesive which were obtained inExamples 1 to 7 and Comparative Examples 1 and 2 were determined bymethods shown below.

(1) Storage Elastic Modulus of Pressure-Sensitive Adhesive

The storage elastic moduli at 23° C. and 80° C. were measured accordingto the method described in the present specification.

(2) Adhesive Strength (Adhesive Strength to Non-Alkali Glass)

The adhesive adhesion to non-alkali glass was measured according to themethod described in the present specification.

(3) Maximum Shear Load

The maximum shear load up to deformation of 4000% was determinedaccording to the method described in the present specification.

(4) Durability of Polarizing Plate with the Pressure-Sensitive Adhesive

The polarizing plate with the pressure-sensitive adhesive was controlledto a size of 233 mm×309 mm by means of a cutting apparatus (Super Cutter“PN1-600” manufactured by OGINO SEIKI CO., LTD.) and applied onnon-alkali glass (“1737” manufactured by Corning Incorporated), and thenit was pressurized in an autoclave manufactured by Kurihara ManufactoryInc. on the conditions of 0.5 MPa, 50° C. and 20 minutes. Thereafter, itwas put under the environment of the following respective durabilityconditions and observed after 200 hours by means of a loupe of 10magnifications to evaluate the durability according to the followingjudging criteria.

◯: no defects in 0.6 mm or more from an outer circumferential end partin four sidesΔ: defects of less than 0.1 mm in abnormality of appearance of thepressure-sensitive adhesive such as lifting, peeling, foaming andstripes in 0.6 mm or more from an outer circumferential end part in anyone side of four sides

X: defects of 0.1 mm or more in abnormality of appearance of thepressure-sensitive adhesive such as lifting, peeling, foaming andstripes in 0.6 mm or more from an outer circumferential end part in anyone side of four sides <Durability Conditions>

Environment of 60° C. and relative humidity of 90%, dry environment of80° C., dry environment of 90° C.

Heat shock test of −20° C. 60° C. for each 30 minutes, 200 cycles

(5) Light Leakage Performance

The polarizing plates with the pressure-sensitive adhesive wascontrolled to a size of 233 mm×309 mm by means of a cutting apparatus(Super Cutter “PN1-600” manufactured by Ogino Seiki Co., Ltd.) andapplied on non-alkali glass (“1737” manufactured by CorningIncorporated), and then it was pressurized in an autoclave manufacturedby Kurihara Manufactory Inc. on the conditions of 0.5 MPa, 50° C. and 20minutes. The polarizing plates with the pressure-sensitive adhesiveswere applied on front and back sides of the non-alkali glass so that apolarizing axis assumed a cross nicol state. It was left standing inthis state at 80° C. for 200 hours. Then, it was left standing for 2hours under the environment of 23° C. and a relative humidity of 50% toevaluate a light leakage property under the above environment by amethod shown below.

MCPD-2000 manufactured by OTSUKA ELECTRONICS CO., LTD. was used tomeasure brightnesses in the respective areas shown in FIG. 3, and abrightness difference ΔL* was determined by an equation:

ΔL*=[(b+c+d+e)/4]−a

(wherein a, b, c, d and e each are brightnesses at measuring points (onepoint in the central part of each area) settled in advance respectivelyin an A area, a B area, a C area, a D area and a E area), and it shows alight leakage property. It is shown that the smaller the value of ΔL*is, the smaller the light leakage is, and usually, if it is less than4.0, the polarizing plate can be used for a liquid crystal display.

(6) Gel Ratio

The pressure-sensitive adhesive having a thickness of 25 μm was sampledin a size of 80 mm×80 mm and wrapped in a polyester-made mesh (meshsize: 200) to weigh precisely only the weight of the pressure-sensitiveadhesive by means of a precision balance. The weight thereof is set asM1. A Soxhlet extractor was used to dip the pressure-sensitive adhesivein an ethyl acetate solvent, and the solvent was refluxed to carry outtreatment for 16 hours. Then, the pressure-sensitive adhesive was takenout and dried in air under the environment of a temperature of 23° C.and relative humidity of 50% for 24 hours, and it was further dried inan oven of 80° C. for 12 hours. The weight of the pressure-sensitiveadhesive alone after dried was weighed by means of a precision balance.The weight thereof is set as M2. The gel ratio (%) is represented by(M2/M1)×100.

Examples 1 to 7 and Comparative Examples 1 and 2

A pressure-sensitive adhesive material (a) having a composition (reducedto a solid content) shown in Table 1 was prepared, and toluene was addedthereto as a solvent to obtain a coating solution controlled to a solidcontent of 20 mass %. The above coating solution was coated on a releaselayer of a polyethylene terephthalate-made release film having athickness of 38 μm (“SP-PET3811” manufactured by LINTEC Corporation) asa release sheet by means of a knife coater so that the thickness afterdried was 25 μm, and then it was subject to drying treatment at 90° C.for one minute to form a pressure-sensitive adhesive material layer.

Then, a polarizing plate comprising a polarizing film provided with adiscotic crystal liquid layer was applied on the pressure-sensitiveadhesive material layer so that the pressure-sensitive adhesive materiallayer was brought into contact with the discotic crystal liquid layer.After 30 minutes passed since applied, a release film side wasirradiated with a UV ray on the following conditions to produce apolarizing plate with the pressure-sensitive adhesive. Thepressure-sensitive adhesive layer had a thickness of 25 μm.

<UV Irradiating Conditions> Electrodeless lamp using an H valve,manufactured by Fusion Co., Ltd.

Illuminance: 600 mW/cm², light quantity: 150 mJ/cm²

“UVPF-36” manufactured by EYEGRAPHICS Co., Ltd. was used for a UVilluminance and light quantity meter.

The evaluation results of the performances of the pressure-sensitiveadhesives and the polarizing plates with the pressure-sensitive adhesiveare shown in Table 2.

TABLE 1 Composition of pressure-sensitive adhesive material (a)Multifunctional Acrylic base polymer (A) acrylic base Molecular monomer(B) Photo- Silane Weight average weight Amount Amount polymerizationPolyisocyanate coupling molecular distribution (mass (mass initiator⁷⁾compound (C)⁸⁾ agent (D)⁹⁾ Kind weight (Mw) (Mw/Mn) part) Kind part)(mass part) (mass part) (mass part) Example 1 BA¹⁾ 1.8 million 4.06 100M-315⁵⁾ 15 1.5 4 0.1 Example 2 BA 1.8 million 4.06 100 M-315 15 1.5 80.1 Example 3 BA 1.8 million 4.06 100 M-315 20 1.5 4 0.1 Example 4 BA1.8 million 4.06 100 R-684⁶⁾ 24 1.5 4 0.1 Example 5 BA 1.8 million 4.06100 M-315 15 1.5 0 0.1 Example 6 BA/AA²⁾ 1.8 million 4.22 100 M-315 151.5 4 0.1 (99.8/0.2) Example 7 BA/AA³⁾ 1.8 million 4.44 100 M-315 15 1.54 0.1 (99.5/0.5) Comparative BA 1.8 million 4.06 100 — 0 — 0 0.1 Example1 Comparative BA/AA⁴⁾ 1.8 million 4.50 100 M-315 15 1.5 4 0.1 Example 2(99/1)

Remarks: 1) BA: polymer of butyl acrylate 2) BA/AA: copolymer of butylacrylate and acrylic acid (mass ratio 99.8/0.2) 3) BA/AA: copolymer ofbutyl acrylate and acrylic acid (mass ratio 99.5/0.5) 4) BA/AA:copolymer of butyl acrylate and acrylic acid (mass ratio 99/1)

5) M-315: tris(acryloxyethyl) isocyanurate, molecular weight=423,trifunctional type (trade name: Aronix M-315, manufactured by ToagoseiCo., Ltd.)

6) R-684: tricyclodecanedimethanol acrylate (“KAYARAD R-684”, molecularweight=336, manufactured by Nippon Kayaku Co., Ltd.)

7) Photopolymerization initiator: mixture of benzophenone and1-hydroxycyclohexyl phenyl ketone in a mass ratio of 1:1, “Irgacure500”, manufactured by Ciba Specialty Chemicals Co., Ltd.

8) Polyisocyanate compound (cross-linking agent, adhesion improvingagent): trimethylol-modified tolylenediisocyanate (“Coronate” L,manufactured by NIPPON POLYURETHANE INDUSTRY CO., LTD.)

9) Silane coupling agent: 3-glycidoxypropyltrtimethoxysilane (“KBM-403”,manufactured by Shin-Etsu Chemical Co., Ltd.)

TABLE 2 Performances of polarizing plate provided Performances ofpressure-sensitive adhesive with pressure-sensitive adhesive Storageelastic Adhesive strength (N/25 mm) Gel Maximum Durability Light leakagemodulus (MPa) 24 hr Rise ratio shear 60° C. 80° C. 90° C. performance23° C. 80° C. (initial value) 168 hr rate (%) (%) load (N) 90% RH drydry Heat shock [ΔL*] Example 1 0.94 0.43 15 16 6.7 96 23 ◯ ◯ ◯ ◯ 0.56Example 2 2.34 1.07 5 5 0 95 21 ◯ ◯ ◯ ◯ 0.52 Example 3 1.41 0.63 6 716.7 94 30 ◯ ◯ ◯ ◯ 0.36 Example 4 0.95 0.41 10 10 0 91 34 ◯ ◯ ◯ ◯ 0.48Example 5 1.2 0.71 3.5 4 14.3 98 20 ◯ Δ ◯ Δ 1.49 Example 6 1.31 0.66 55.5 10.0 97 32 ◯ ◯ ◯ Δ 0.78 Example 7 1.31 0.66 16 18.9 18.0 96 36 Δ ◯ ΔΔ 0.78 Comparative 0.11 0.09 7 7 0 2 8 X X X X 0.39 Example 1Comparative 0.87 0.73 21.5 42 95.3 96 58 ◯ ◯ ◯ ◯ 0.88 Example 2

INDUSTRIAL APPLICABILITY

The pressure-sensitive adhesive of the present invention for polarizingplates is suitably applied to a polarizing plate, particularly apolarizing plate integrated with a viewing angle expanding film or apolarizing plate comprising a retardation film laminated thereon and canapply the above polarizing plate on a liquid crystal cell with goodadhesion, and it has the characteristic that a liquid crystal displayobtained therefrom is less liable to cause light leakage even under theenvironment of high temperature and high humidity. When an applyingposition is deviated, the polarizing plate can be peeled off again evenafter some time passes since applied, and the expensive liquid crystalcell can be reused.

1. A pressure-sensitive adhesive for polarizing plates, which isprepared by irradiating a pressure-sensitive adhesive materialcomprising (A) an acrylic base polymer comprising a monomer having acarboxyl group in a monomer composition ratio of 0.5 mass % or less and(B) an active energy beam-curable compound with an active energy beamand which has a storage elastic modulus (G′) of 0.3 MPa or more at 23°C.
 2. The pressure-sensitive adhesive for polarizing plates as describedin claim 1, wherein the storage elastic modulus (G′) at 23° C. is 0.3 to15 MPa.
 3. The pressure-sensitive adhesive for polarizing plates asdescribed in claim 1 or 2, wherein the storage elastic modulus (G′) at80° C. is 0.3 MPa or more.
 4. The pressure-sensitive adhesive forpolarizing plates as described in claim 3, wherein the storage elasticmodulus (G′) at 80° C. is 0.3 to 10 MPa.
 5. The pressure-sensitiveadhesive for polarizing plates as described in claim 1, wherein it isused for applying a polarizing plate on a liquid crystal glass cell. 6.The pressure-sensitive adhesive for polarizing plates as described inclaim 1, wherein the active energy beam-curable compound of thecomponent (B) is a multifunctional (meth)acrylate base monomer having amolecular weight of less than
 1000. 7. The pressure-sensitive adhesivefor polarizing plates as described in claim 6, wherein themultifunctional (meth)acrylate base monomer has a cyclic structure. 8.The pressure-sensitive adhesive for polarizing plates as described inclaim 1, wherein a content proportion of the component (A) to thecomponent (B) is 100:1 to 100:100 in terms of a mass ratio.
 9. Thepressure-sensitive adhesive for polarizing plates as described in claim1, wherein the pressure-sensitive adhesive material further comprises(C) a cross-linking agent.
 10. The pressure-sensitive adhesive forpolarizing plates as described in claim 1, wherein thepressure-sensitive adhesive material further comprises (D) a silanecoupling agent.
 11. The pressure-sensitive adhesive for polarizingplates as described in claim 1, wherein an adhesive strength tonon-alkali glass is 0.2 to 20 N/25 mm.
 12. The pressure-sensitiveadhesive for polarizing plates as described in claim 11, wherein a risepercentage of the adhesive strength to non-alkali glass after 168 hourspass since applied is 20% or less based on the initial value.
 13. Thepressure-sensitive adhesive for polarizing plates as described in claim1, wherein a maximum shear load at a distortion of 4000% or less inapplying the polarizing plate on non-alkali glass at an applying area of100 mm² (10 mm×10 mm) and measuring a shear load at a shearing rate of0.1 mm/minute is 70 N or less.
 14. The pressure-sensitive adhesive forpolarizing plates as described in claim 1, wherein a gel ratio is 85% ormore.
 15. A polarizing plate with a pressure-sensitive adhesive,characterized by having a layer comprising the pressure-sensitiveadhesive as described in claim 1 on a polarizing plate.
 16. A productionprocess for the polarizing plate with the pressure-sensitive adhesive asdescribed in claim 15, comprising applying a polarizing plate on apressure-sensitive adhesive material layer provided on a release layerof a release sheet and then irradiating a release sheet side with anactive energy beam.
 17. A pressure-sensitive adhesive sheet prepared byinterposing the pressure-sensitive adhesive for polarizing plates asdescribed in claim 1 between two release sheets so that thepressure-sensitive adhesive is brought into contact with release layersides of the release sheets.